1. Field of the Invention
With reference to the classification of art as established in the United States Patent & Trademark Office the field of art to which this invention pertains is found in the general Class of "Geometrical Instruments (Class 33) and more particularly in the subclass of "distance measuring" (subclass 125 R). Also of note is the art in the further subclass of "opposed contacts" (subclass 143 R).
2. Description of the Prior Art
Micrometers which utilize a precision ground lead screw running in a precision nut are well known. In these devices the rotary motion of the barrel is read upon a scale inscribed upon the rotary anvil or a shell carried thereby. These micrometers, of course, are well known and for many years have been a standard in machine shops for use in measuring workpieces. Micrometers, having heads with optical rotary encoders attached to the lead screw, and with displayed readout, have been brought to the market in the past few years. Vernier calipers and height gages using precision-engraved scales are also well known and are particularly useful in marking measurements of relatively long distances such as for measuring from zero to twelve inches or from zero to other units of a longer length. In the use of micrometers having a precision lead screw there have been many attempts and patents directed toward controlling the advancement of the lead screw to provide a determined amount of drive friction so that neither an excessive squeeze nor too light an engagement or grip on the object to be measured is provided in the use of the micrometer. It is well known, for example, that different inspectors well skilled in the use of a lead-screw type of micrometer and using the same micrometer under the same conditions may vary as much as two or three ten-thousandths of an inch in reading measurement for the same workpiece. This variation, of course, occurs because of the head manipulation provided by the inspector himself.
In the same manner the use of a vernier caliper and its precision scale depends upon the accuracy of the scale as well as the skill of the inspector in setting the jaws of the vernier caliper. In addition to the requirements of physical dexterity in using these two well known types of measuring instruments there is also the potential visual tricks played upon the inspector in reading the setting of the barrel or reading of the vernier scale wherein numbers are transposed. Sometimes it becomes a matter of aligning or reading the degree of coincidence of a pair of lines as to which line is the nearest to the precise reading of the scales. Precision end measuring rods, gage-blocks (also known as Jo-blocks) and like precision measuring members are, of course, well known. The difficulty in using such type of devices is the necessity of accumulating the precise desired quantity of these precision-made measuring members. Dial indicators as measuring tools are also well known; however, their accuracy is again subject to many problems of wear and the maintenance of the gears and movable rack as well as the reading of the dials and the initial setting of the indicator.
In the present invention it is contemplated that a micrometer having a fixed anvil carried by a frame will have a movable anvil which is moved to a closed condition by means of a constant force spring. The operator or user of the micrometer pulls or draws the movable anvil from the fixed anvil so that the piece to be measured is brought between the anvils, after which the movable anvil is released so that it is moved to and against the piece being measured under the influence of the predetermined constant force spring. After the movable anvil has been brought to rest against the workpiece to be measured, an electrical readout visually displays the precise measurement between the fixed anvil and the movable anvil. In gages such as height gages modifications of the frame are made and the same measuring means are provided.
It is, of course, well known to use glass or metal scales to measure the travel of the workstables of machine tools. These scales and other measuring systems are usually fixed in relation to a frame and the scale itself is directly read in relation to the position of the indicating device as it is moved along the bed or table of the machine or work member which is used to measure the amount of travel of the machine tool or workpiece. Such readings do not convert the travel into digital readouts except some of the latest electro-optical linear encoders.
Rack and pinion systems used for driving rotary encoders are known as well as tape systems using a tape drawn around a precision pulley. It is also known to utilize a rotary movement of a precise roller over the face of a machine tool workstable. However, insofar as is known, these systems tend to develop both random and accumulative errors arising from dirt, linear expansion or contraction because of changes in temperature or because of wear or slippage, causing these measuring systems to lose their precision even if the accuracy is initially provided.
In particular, as far as is known, there has been no tape system for a hand held micrometer vernier or height gage using a tape stored in a spring-loaded spool with the tape fed from the spool. Where the rotation of a precision roller is caused by said roller being driven by movement of the roller along the workpiece, this type of system in a micrometer or caliper would require that the workpiece being measured would be free of oil, dirt or a combination thereof. This, of course, cannot be guaranteed although essential in a very precision instrument.
In the present invention the electro-optical digital positioning micrometer, or linear digital gage utilizes a precision screw which is caused to be rotated and with it a radially arranged interrupter disc is rotated to cause electrical pulses to be generated and fed to a digital readout. Each micrometer indicator is disposed to read the linear travel of the movable anvil. The screw in its mounted condition within the frame is moved to the closed condition in a constant force spring and during measuring operations the movable anvil is urged to a close condition. This anvil is maintained by this force spring in a fixed relation to the fixed anvil as the movable anvil is moved to a measuring condition on the workpiece to be measured. The screw and the rest of the movable portions of the micrometers are maintained in a substantially sealed enclosure condition so that the accuracy initially built into the micrometer will be maintained throughout its use and operation.